joint:slider not working

Hi all, Since URDF does not support closed loop links I closed the loop using a hidden joint:hinge in the .gazebo.xacro file for my robot, following some ROS answers for a similar question. ${link}${prefix}_${suffix}_wheel_HubTop${prefix}_${suffix}_wheel_HubTop0 1 00 0 -0.045 However, when I change the joint:hinge to joint:slider the model no longer has this joint in the gazebo (show joints). ${link}${prefix}_${suffix}_wheel_HubTop${prefix}_${suffix}_wheel_HubTop0 1 00 0 -0.045 Why is that? Any workaround? Also, joint:screw didn't work either. Thank you Cheers! CS